Which engine was standard in the Rasmus 35, and what are its common weak points?
I'm looking at a Hallberg-Rassy Rasmus 35 advertised with its original 75 hp Volvo Penta diesel. Which engine should that be, and what expensive problems should I check for before buying?
Answer
The usual factory diesel in the Hallberg-Rassy Rasmus 35 was the Volvo Penta MD21, a four-cylinder, Peugeot-based engine commonly rated at 75 hp. Its main buying risks today are deterioration of the cooling and wet-exhaust systems, damage from past overheating, and difficulty finding some marine-specific parts.
Identify the fitted engine
Start with the engine identification plate and service records. Rasmus production spanned the late 1960s and much of the 1970s, so check the build year, engine version and any replacements. Both MD21A and MD21B designations occur; an advert saying simply "original Volvo" tells you too little.
The MD21 has a freshwater circuit cooled through a seawater heat exchanger. Freshwater cooling protects the engine internally only if the coolant has been maintained and the exchanger remains sound.
Do not confuse it with the later Volvo Penta MD22 or the three-cylinder 2003T fitted to other Hallberg-Rassy models. Their servicing requirements and parts differ. A Rasmus with a Beta or Yanmar has been repowered, so assess the installation as well as the engine.
Record the engine and gearbox model and serial numbers before ordering parts. Horsepower alone will not identify the correct impeller, thermostat, gasket or exhaust component.
Inspect cooling and exhaust
Check the cooling system first. A restricted seawater circuit can turn a serviceable old diesel into a major repair, and a new impeller says nothing about the condition of the rest of the system.
- Seawater intake and strainer: check for obstruction, air leaks and hoses that soften or collapse under suction.
- Seawater pump: inspect the cover, shaft and seals for wear or leakage. Trace any missing impeller blades; fragments can obstruct the exchanger inlet.
- Heat exchanger: look for leaking end seals, salt deposits and signs of neglected cleaning. A leaking tube stack can let seawater and coolant pass between the circuits.
- Exhaust mixing elbow: check for internal corrosion and carbon restriction, even if the outside looks sound. Restricted flow increases exhaust back-pressure and can contribute to overheating.
With the engine cold, inspect the coolant level and condition, then watch the temperature during a sea trial under load. Persistent coolant loss, coolant expelled from the header tank, or overheating at cruising power needs diagnosis before purchase.
Never remove the coolant pressure cap while the engine is hot.